The HIV/AIDS epidemic in Russia has been concentrated largely among the high-risk core groups of injection drug users (IDU) and commercial sex workers (CSW), and the overlap of these two populations is substantial. Recent reports of increasing prevalence of HIV due to sexual transmission in St. Petersburg suggest that spread of HIV into the general population may be increasing. However, little is known about the potential for or risks associated with sexual transmission from CSW to their sex partners, both clients and non-clients, who may be a "bridge" to the general population. As a first step in exploring the potential for a generalized HIV epidemic in Russia, we propose a new collaboration between experienced US and Russian researcher teams to develop methods to study sexual transmission of HIV from female CSW to their sex partners (both clients and non-clients) by including sex partners in research studies. Our specific aims are to: 1. Understand the variety of different types of sex partners, both clients and non-clients, of street-based CSW in St. Petersburg, Russia; 2. Develop and evaluate methods for recruiting both client and non-client sex partners; 3. Pilot test data collection methods, both quantitative and qualitative, for validation and hypothesis generation. To understand the variety, we will begin with in-depth, qualitative interviews of key informants including CSW, their sex partners, police, sexually transmitted disease clinic providers, and outreach social workers. This will be followed by development and implementation strategies for sex partner recruitment - including referral by CSW, time-location sampling, snowball methods, and the Internet - followed by and survey interviewing of these men. This application is directly responsive to several stated objectives in this RFA, including increasing our understanding of the intersection between commercial sex, drugs of abuse, HIV risk; and factors that influence HIV transmission dynamics from high risk to low risk groups. Furthermore, this application will foster a new collaboration between accomplished US and foreign institutions by bringing together investigators from Yale University Center for Interdisciplinary Research on AIDS and the NGO Stellit. These investigators share a common interest in HIV prevention in Russia, in particular among CSW and IDU, and have complementary experience and skills to contribute to this goal. This work will catalyze our collaborative relationship and help to ensure the continued development of innovative research and intervention development. [unreadable] [unreadable] In this application, we propose a research plan to increase our understanding of potential HIV bridging from the high risk group of drug using commercial sex workers to the general population through sexual transmission in St. Petersburg, Russia. This study is directly relevant to the public's health because results will be used to develop urgently needed prevention interventions for female CSW and their male sex partners for promoting their own health and reducing the potential magnitude of a generalized epidemic. [unreadable] [unreadable] [unreadable]